Process and apparatus for recovering silver from photographer&#39;s spent hyposulphite solution



Patented 17, 15921 y i ERNEST K. GIEJFEN, OF SALIDA, COLORADO.

onse ann ennemis non covnnme srnvnia Enom monroe, 1:.. i.

HYPOSULPHITE SOLUTION.

application sied september 1e, 1925. serial no. 57,455. s

' This invention relates to a process and apparatus for recoveringsilver from the more or less exhausted photographers solutions commonlyknown as hypo-sulphite of s soda. An object of the invention is theprovision of a device in which the exhausted photographers solutions ofhypo-sulphite of. soda are placed with a special equipment of 1o.positive and electric plates disposed in the solution which in thepresent case forms electrolyte whereby the silver will lbe depositedupon the positive electrode without any ossibility of the silver beingacted i5 upon y hydrogen sulphide which is formed when the hypo-sulphitesolution acts on the positive element, since the gas, after forma--tion, is directed away-from v the solution.

Another object of the invention is the provision of a device forrecovering silver from exhausted photographers solution of hylpo-sulphteof soda and in which the sul- P ite solution is used as an electrolyteand a pair ofelements representing positive and ae negativeare so'placedin the electrolytevto' produce a current and recover thefsilver on thepositive element that the silver when se arated will not be affectedbyhydrogen su phide gas since the liydrogensulphide 43o developed in theelectrolyte by the breaking i so that when the circuit is closed thesilver will be liberated and be deposited on the ositive element of thebattery, a resistance ing employed inthe circuit for aiding inmaintainin the'voltage constant until -all 45 the silver 1s depositedlso that achemical action is prevented in the liquid which normallycauses the production of hydrogen sulphide gas `with the consequentprecipitation of sulphide of silver.

i This invention will be best understood from a consideration of thefollowing de- Itailed description, in view of the accompanyf the neg ingdrawing forming apart of the specification; neverthelessit is to beunderstood that the invention is not confined to the disclosure, beingsusceptible of such changes and modifications which shall-*define nomaterial departure from the salient features of the invention asexpressed in the 'appended claims.

In the drawings: Figure 1 represents more or less -diagrammatically avertical section of a device for carrying out my process for therecovery of silver from exhausted hypo-sulphite solutions. I

Figure 2 is a transverse section of the bag taken along the line 2 2 ofFigure 1.

Referring more particularly to the dravvings, 1 designates a casing`which may be made of glass or some other material not affected by acidsand which has (an upper flanged portionl 2 forming a. bead andprojecting laterally from the upper end of said container. Anyconvenient vessel such as an extra fixing tank or barrel may b eemployed by the photographer for the casing 1. The

container is adapted to be filled "with the` more or less exhaustedsolution of hyposulphite of soda to the level indicated by the numeral 3and into which is inserted at its upper end a porous bag 4 which may beof'canvas or any other material suitable for the purpose. An elementformed of a zinc plate is inserted within the bag and forms fill thebag.

The positive element 7 is located at the bottom of the 'container landis in the shape ative pole of the battery.- Thev zinc lplate is of sucha size as to approximately of a copperlscreensurrounded by a secondfiber netting 8 such as 1/4-inch lisli netting, for the support of thecopper screen and the silver that collects thereon. The netting8completely encloses the element 7 An insulated wire 9 connects thepositive element 7 with one end of a resistance 1 0, the other end ofthe resistance being con' nected by a Wire 11 to a plug 12. An inisulated wire13 connects the negative electrode 5 with the plug 12. Said.plug is adapted to form a connection for closing the circuit between thenegative element 5 and the positive element 7 so that a current willpass therethrough and cause disintegration of the liypo-sulphitesolution in the container 1 which acts upon the zinc 6 in the bag orcasing- 4. The current, it Will be seen, passes in the liquid from thenegative element to the positive element 7 and out of the liquid throughthe connecting wire 9 from the positive element to the negative element5. The zinc being the active element thus forms the negative pole of thebattery. A cord or rope 14 is connected to the bag 4 and bent around theflanged upper end 2 of the container 1 and a Weight .17 susi pended bythe rope outside oi the container is adapted to maintain the bagadjacent thev top of the container so that an air space i6- is providedabove the level 3 of the liquid and the top of said bag.

In the operation of my device theqcon tainer 1 is filled tol the levelindicated at 3 with the hypo-sulphite solution and the bag 4 is likewisefilled to the'point indicated by the level of the liquid in thecontainer l. The action of the hypo-sulphite solution on the zinc in thebag initiates the action of the battery for the recovery of thesilverfrom the whole solution. A woven copper element 7 is, in a shortperiod of time, covered with a thin silver coating providing a silverelement. The silver. from the eX- hausted -hypo solution in the bagbeing replaced by the zinc forming probably a zinc' hypo-sulphite orother zinc salts. Thus will be seen that the essentials of a Voltaiccellv are provided, that is a silver electrode surrounded by a silversalt, and a zinc elec trode surrounded by a zinc salt or salts, and

thetwo separated by a porous partition or canvas bag and the whole spacebetween the elements 5 and 7 being occupied by a concentrated solution.of sodium hypo-sulplnte which has not been saturated with the silver,whereby the internal resistance of' the'Voltaic cell is reduced. Anelectric current 1s thus set up between the negative element 5 The zinc,ions go into solution and force the positive silver ions onto thecopper screen 7. This action2 is maintained. until thefsilver isexhausted from the solution and deposited as metallic silver on lthescreen 7 provlded, however, thatfthe. external circuit passes throughA asuitable resistance such as 10 .and

which resistance must be atleast such thatthe Voltaic cell. may maintainapproxi- Amately its full voltage until all the silver is deposlted onthe copper screen 7. The resistance is absolutelyfessential sincewithout ita. chemical ,action would take placelwhich would causehydrogen sulphde'gas to be formed and which would cause theprecipitation of silversulphide so that the silver coated copper screen7 would become black and prevent the continuous deposlt'of the silverfrom the solution.

Furthermore it must. be borne in mind that unless the zinc element 5 wasenclosed within the' porous bag 4. silver would notkbe depositedjon thescreen 7 for any length of time because of the fact that the bag pro-.70

vides a means for preventingl the hydrogen sulphide from entering thesolution in the container l and attacking the silver in solution.

What I claim is: y y X l. A device for recovering metallic silver fromphotographers spent hypo-sulphite solution comprising acontainer adaptedto be partially filled with a liypo-suphite solution,

a porous bag supported in the container to a predetermined depth in thesolution, metal in the bag forming a negative element of a voltaic cell,a positive element placed inthe solution remote from the negativeelement, an insulated external connection .between the 85 positiveelement and the' negative element in the bag, and a resistanceinterposed in the wire.

2. A'device vfor recovering metallic silver from photographers spenthypo-sulphite so- 00 lution comprising a container adapted to bepartially filled with a hypo-sulphite solution, a porous` bag' sup ortedin the container to apredetermined) depthin the solution, a metal in thebag forming a negative 06 element of a voltaic cell, a positive elementhaving a large metallic collecting surface placed vin the solution, aninsulated wire connecting the positive elementl with the negativeelementin the bag, and a resistance interposed inthe wire.

3. A device for recovering metallic silverv from photographers spenthypo-sulphitesolution and comprising a container adapted to be partiallyfilled with a hypo-sulphite solution, a porous bag supported in thecontainer to a predetermined depth in the solu ltion so that a portionof the bag will be maintained above the level of the liquid, a metal inthe bag forming a negative element of a voltaic cell, a positive elementplaced in the solution remotel from the 'negative element, an insulatedexternal connection between the' positive element' and the negative.element having -a predetermined ohmicr resistanc'e, said positiveelement comprising a copper screen, and a fiber netting surrounding saidscreen. a

4. A device for recovering metallic silver, from photographers spenthypo-sulphite so- 4lution comprising a container adapted .to bepartially filled'iwith a hypo-sulphite solution, a porous bag supportedin the container to a predetermined depth in the solution so that aportion of the bag will be maintained .125 above the level ofthe liquid,means for adjustablysupporting the bag in said solution, a metal inthebag forming a negative elementpoha voltaic .cell a `positive element-`placed in the solution 'adjacent the bottom of A130 container, aninsulated wire connecting the la/tionnin the solution 'to form 1avoltaic cell i positive elementwith the negative elementandoonnectinmlsaid elements` externally in the bag, and a` redetermnedohmic rethrough an o c resistance whichp will l sistance interposed mthe wire. maintain the maximum'voltage between said 5. A. process forthe recovery of `si1ver elements during deposition of silver upon lfromspent hypo-sulphite solutions which oneof said elements..

ERNEST K. GiFFEN,

comprises immersing elements in remote re-

